In the related art, a semiconductor device has been known which includes a diode as an overheat protection function in order to prevent the thermal breakdown of a MOS (metal-oxide film-semiconductor insulated gate) semiconductor element, such as a metal oxide semiconductor field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT). Specifically, in order to protect the MOS semiconductor element from overvoltage, a plurality of diodes or bidirectional diodes are provided between the gate and the source or between the gate and the drain.
As the MOS semiconductor device according to the related art which includes the temperature detecting diode, a device has been proposed in which a capacitor is formed so as to overlap a temperature detecting diode in the thickness direction of a semiconductor substrate and is electrically connected in parallel to the temperature detecting diode, in order to reduce radio frequency noise acting on the temperature detecting diode (for example, see the following Patent Document 1).
Another MOS semiconductor device has been proposed in which a protective capacitor or a diode and a temperature detecting diode are formed on the same substrate and the protective capacitor or the diode is connected in parallel to the temperature detecting diode, in order to improve the static electricity resistance of the temperature detecting diode (for example, see the following Patent Document 2 and Patent Document 3).
Another MOS semiconductor device has been proposed which includes a capacitor for preventing a change in characteristics or damage when a voltage that is higher than the breakdown voltage of a protective diode for a temperature detecting diode is applied to the protective diode in the reverse direction due to, for example, electrostatic discharge (for example, see the following Patent Document 4).
Another MOS semiconductor device has been proposed in which, in order to prevent the arrangement position of a temperature detecting diode from being limited by a diffusion structure in a portion below the temperature detecting diode (a portion which is closer to a semiconductor substrate than the temperature detecting diode), an insulating film is formed on the semiconductor substrate, a conductive layer is formed on the insulating film, the temperature detecting diode is formed on the conductive layer, with an insulating film interposed therebetween, and the temperature detecting diode is electrically insulated from the semiconductor substrate (for example, see the following Patent Document 5).
As another MOS semiconductor device, a device has been proposed in which two polysilicon diodes having an insulating film interposed therebetween are formed on an insulating film formed on the main surface of a semiconductor substrate main surface and the insulating film between the polysilicon diodes is used as a capacitive component region (for example, see the following Patent Document 6). In the following Patent Document 6, the insulating film serving as a capacitor has an opening portion and the polysilicon diode on the insulating film and the polysilicon diode below the insulating film are connected to each other through the opening portion. As such, since the two-layer polysilicon diodes are formed, the area of the polysilicon diode is reduced and the capacitor is electrically insulated from the semiconductor substrate. Therefore, stable capacitance is obtained.
As another MOS semiconductor device, a device has been proposed in which a plurality of stripe-shaped or rectangular zener diodes are formed in a gate pad and are electrically connected in parallel to each other, thereby improving static electricity resistance (for example, see the following Patent Document 7). In addition, as a method for producing a MOS semiconductor device, a production method has been proposed in which, in order to reduce the number of steps when a polysilicon diode, a capacitor, a resistor, and an insulated gate semiconductor element are formed on the same semiconductor substrate, a gate oxide film and an oxide film thicker than the gate oxide film are formed, a polysilicon layer is formed thereon and is then patterned to form a gate electrode, the diode, the capacitor, and the resistor (for example, see the following Patent Document 8).
As another method for producing a MOS semiconductor device, a method has been proposed in which an insulating film between a temperature detecting diode and a semiconductor substrate and a gate oxide film are formed in the same step (for example, see the following Patent Document 9).